try.go

gistfile1.txt

package main

import (
	"fmt"
	"regexp"
	"sort"
	"strconv"
)

type Tracker struct {
	store map[string][]int
}

func (t *Tracker) Alloc(name string) string {
	if t.store == nil {
		t.store = make(map[string][]int)
	}
	r, ok := t.store[name]
	if !ok {
		t.store[name] = make([]int, 0)
		r = t.store[name] // avoid double lookup
	}
	next := nextServerNum(r)
	r = append(r, next)
	t.store[name] = r
	return fmt.Sprintf("%s%d", name, next)
}

var reg = regexp.MustCompile(`([a-z]+)(\d+)`)

func (t *Tracker) Dealloc(name string) {
	if t.store == nil {
		return
	}
	arr := reg.FindStringSubmatch(name)
	name = arr[1]
	num, err := strconv.Atoi(arr[2])
	if err != nil {
		// TODO return
		panic(err)
	}

	res, ok := t.store[name]
	if !ok {
		return
	}
	res = removeElem(res, num)
	t.store[name] = res
}

//TODO do inplace
func removeElem(arr []int, i int) []int {
	var res []int
	for _, j := range arr {
		if j == i {
			continue
		}
		res = append(res, j)
	}
	return res
}

func nextServerNum(input []int) int {
	sort.Ints(input)

	if len(input) == 0 {
		return 1
	}
	if input[0] != 1 {
		return 1
	}

	for index, val := range input {
		next := -1
		if index < len(input)-1 {
			next = input[index+1]
		}
		if next == val+1 {
			continue
		}
		if next != -1 {
			return val + 1
		}
	}
	return input[len(input)-1] + 1
}

func assert(input []int, output int) {
	if nextServerNum(input) != output {
		fmt.Println(input)
		panic(input)
	}
}

func main() {
	assert([]int{1, 2, 3}, 4)
	assert([]int{1, 3}, 2)
	assert([]int{1, 2, 4, 5}, 3)
	assert([]int{2, 4, 5}, 1)
	assert([]int{1, 4, 5}, 2)
	assert([]int{}, 1)
	fmt.Println("all is well")
	t := &Tracker{}
	for i := 0; i < 10; i++ {
		fmt.Println(t.Alloc("api"))
	}
	t.Dealloc("api5")
	fmt.Println(t.Alloc("api"))

	// for i := 0; i < 10; i++ {
	// 	fmt.Println(t.Alloc("site"))
	// }
}